Section 1 of 6What internal energy is
Two components
- Two components Internal energy is the sum of the kinetic energy stores and the potential energy stores of all the particles in a system.
Kinetic part
- Kinetic part Due to the random motion of the particles: they vibrate in a solid and move freely in a liquid or gas.
Potential part
- Potential part Due to the forces of attraction between particles, which depend on how far apart they are.
Not the same as temperature
- Not the same as temperature Temperature relates only to the average kinetic energy of the particles,
- while internal energy also includes potential energy and depends on the mass.
Section 2 of 6Heating a substance
1Energy is transferred
- Energy is transferred Thermal energy is supplied to the system by heating, raising its internal energy.
2Particles gain energy
- Particles gain energy The energy goes either to kinetic stores or to potential stores.
3Temperature rise or state change
- Temperature rise or state change If the kinetic energy rises, the temperature increases.
- If the potential energy rises, the particles move apart and the substance changes state.
Section 3 of 6Particle models of the states
| State | Particle arrangement | Movement | Forces |
|---|---|---|---|
| Solid | Regular pattern, touching | Vibrate about fixed positions | Strong attraction |
| Liquid | Irregular, touching | Move past each other | Weaker attraction |
| Gas | Far apart, random | Move quickly and freely | Almost no attraction |
Section 4 of 6Changes of state
1
At the melting point, supplied energy breaks the bonds holding the solid together, so potential energy increases while the temperature stays constant.
2
At the boiling point, energy lets particles escape from the liquid completely, again with a constant temperature.
3
These changes are physical, not chemical, and the mass of the substance is conserved.
4
When the process is reversed, by cooling, the internal energy decreases and the substance freezes or condenses.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Internal energy | The total kinetic and potential energy of all the particles in a system. |
| Kinetic energy store | Energy due to the motion of particles. |
| Potential energy store | Energy due to the positions of particles relative to each other and the forces between them. |
| Temperature | A measure of the average kinetic energy of the particles. |
| Change of state | A physical change such as melting, boiling, condensing or freezing. |
Section 6 of 6Exam technique
1
Saying temperature and internal energy are the same thing; a large cool lake has more internal energy than a hot cup of tea.
2
Writing that particles themselves melt or expand when heated — they just move or separate more.
3
Forgetting the potential energy component when explaining why temperature stays constant during a change of state.
4
Thinking cooling a substance removes particles; the number of particles stays the same.
البيولوجيا الجزيئية — أسرار تخليق البروتين
مقارنة اتجاهات الإنزيمات
قواعد اتجاهات البلمرة ومضاد الكودون
- إنزيم بلمرة RNA: يبني دائماً في الاتجاه 5′ → 3′، ويقرأ شريط القالب فقط في الاتجاه 3′ → 5′.
- كودون البدء: AUG يقابله مضاد كودون UAC ويشفر للميثيونين أول حمض أميني.
- كودونات الوقف: UAA, UAG, UGA ليس لها tRNA يقابلها، بل يرتبط بها بروتين عامل الإطلاق (Release Factor) لإنهاء الترجمة.